The invention relates to a system and method for a surface strain gauge, which can provide an intelligent smart surface strain gauge and which has direct application to wind turbine structures and wind turbine blades and wind turbine struts. The invention is equally applicable to other airfoil structures such as aircraft wings and aircraft fuselages.
In particular, the invention teaches a method for making use of the properties of carbon fibre reinforced epoxy to provide the basis of a smart surface strain gauge. According to the invention, the material can be integrated into the surface of a structure in an array comprising separate sheets of carbon fibre reinforced epoxy which are linked together and which each comprise a separately addressable element such as a microcontroller wherein the microcontrollers are connected to a power supply and to a central bus which itself links to a central system controller.
Differential measurements of the resistance of separate carbon fibre reinforced epoxy sheets may be determined in real time as well as the resistance between two or more sheets. In this way real time dynamic load monitoring can be performed and compared with original values determined at time of manufacture to provide data on fatigue of the structure with time before damage and failure occurs.
Continuous carbon fibre is easily incorporated into composite structures and so allows sensing of both real time strain and cumulative damage covering large sections of the structure and so providing monitoring of the current safety of the structure with a statistically high reliability of detection.
Generally, strain gauges are known but these often involve the use of strain sensors such as piezoresistive or piezoelectric sensors. Such sensors tend to degrade the mechanical properties of the composite if added.
Recently the properties of carbon fibre reinforced epoxy have been determined to be ideally suited to being suitable for a strain gauge. Whereas a structure with embedded or attached sensors is only smart in the vicinity of each sensor, if a sheet structure of carbon fibre reinforced epoxy is integrated into the surface of the said structure instead, the sheet offers the capability to act as a smart sensor across the entire surface. The electrical resistance of a short carbon fibre epoxy matrix composite increases reversibly upon tension and decreases reversibly upon compression.
It is towards the creation of an advanced strain gauge system, which has the capability to perform differential dynamic load monitoring through direct addressing of separate surface elements of carbon fibre reinforced epoxy and provide this data to a central system controller and this determine any fatigue of a structure that the current invention is directed.
No systems are presently known to the applicants, which address this market need in a highly effective and economic way.
Further to the limitations of existing technologies used for designs for smart strain gauges, and so far as is known, no optimised system and method for an intelligent dynamic load monitoring strain gauge which has suitable application to airfoil structures such as wind turbines, struts and aircraft wings is presently available which is directed towards the specific needs of this problem area as outlined.